Tuesday, April 29, 2014

Delta Bot: First Motion!

I've been fighting with the Arduino Mega and RAMPS 1.4 electronics for the last month or so on the RepRap Rostock clone I'm building. Every time I plug everything in - RAMPS into the 12v power supply, Arduino into the PC via USB cable - the 5V voltage regulator on the Arduino overheats. And not just a little- enough to get hot enough to smoke and eventually pop. I burned out the regulator on one Arduino by leaving it plugged in too long. I ordered a strip of replacement surface mount 5V regulators from ebay- hopefully replacement on the burned out Arduino isn't too hard.

Burned out Arduino Mega 2560 5v regulator- upper left next to the power plug. Note the big hole blown in it!

I tried searching the forums and general google searching to try and find the root cause. No luck- and forum responses were generally about making sure the power supply polarity was correct, etc. After finishing the searches and looking through reprap.org's RAMPS 1.4 page, I thought a possible cause might be some mismatch between the 12v power supply and the power supplied by the USB cable from the PC. The D1 diode on the RAMPS board allows the 12v power supply to also supply power to the Arduino. If the D1 is cut, the Arduino must be powered off the USB- but it wouldn't receive any potentially troublesome power from the RAMPS board. So, I decided to cut the D1 diode. Worst case I can solder in a new diode.

It was pretty tough to actually cut the D1- it's tucked way down next to the stepper driver sockets. (under the "x" and "y" stepper drivers) I ended up cutting it using the tip of an x-acto knife.

D1 is the small black / silver cylinder in the center left of the frame
I plugged everything back in- and no smoke! I left it plugged in with the 12V power supply and USB connected for five minutes, and monitored the 5F voltage regulator temperature with my finger. It seemed to stay cool- so I fired up Repetier Host and tried to make it go:

Thursday, April 3, 2014

Delta Bot Build: cooling fan & magnetic bearings

Finally- more progress on the "snowstock" delta bot 3D printer! 

I've uploaded the files of all parts shown in this blog post to the "Snowstock" page on Thingiverse.

.STL and solidworks 2013 .prt files are located at: http://www.thingiverse.com/thing:214848

Cooling Shroud
One of the things I learned from using and modifying my MendelMax 1.5 is that a cooling fan really, really helps with part quality- particularly with bridging and small features. So, the snowstock will have a part cooling fan from the start. 

Fan shroud wth 40mm fan mounted and ready to go

Mounted and ready to go

The assembly looks great, but the Traxxas rod ends introduced much more slop than I'd like. Ideally there should be zero backlash / slop in the print head. As assembled, it had at least a quarter inch of total play at the nozzle- unacceptable for a quality print. So, I decided to implement magnetic bearings right away and not as a future upgrade.

Assembling and  installing the magnetic bearings 

I chose to design and print ABS endcaps to epoxy onto carbon fiber rod to hold the M5x15 SHCS's. Other examples of magnetic bearings I've seen online have glued the 10mm spherical magnets to the ends of the carbon rods. That might work, but it seems less secure and messier than just using two screws per joint, one on each side of the ball magnet. Each screw is then threaded into the respective component.

Endcap ready for screw installation and epoxying 

M5x15 SHCS installed- note head was dished out using a 10mm ball end mill for a higher strength joint with the 10mm rare earth magnets
The 10mm ball end mill was sourced from ebay- about $10 including shipping from China. The M5x15 SHCS were from McMaster Carr. One note- you'll want to use black oxide coated steel screws- not stainless steel. Stainless screws are not very magnetic, and you'll probably have problems getting your system to hold together if you try them. The cheap 10mm ball end mill was barely good for dishing the heads of the 24 screws, even with good lubrication.

Dishing out the M5x15mm SHCSs

All 6 rods, assembled and ready to go
Carriage mount installed

Joint detail shown- the silver ball is a 10mm spherical rare earth magnet from e-bay
There are plenty of sources for 10mm spherical magnets on ebay, just search for: "Nickel plated Neodymium Sphere Magnet 10mm N35 balls"

Magnetic arms assembled
I have yet to actually power up and run the printer- I still need to design, print and install the extrusion mechanism. But, even so, I think the magnetic bearing upgrade was worth while. The Traxxas rod ends had far too much slop, I'm sure it would have been very difficult to achieve a decent print quality. The magnetic bearings have zero slop, and also very securely hold the mechanism together. As long as there isn't any sort of long term wear issues I'm sure they will work great.